Break it down...how? What does Duran do that Floyd has NEVER been able to handle? And what does Floyd do that Duran has NEVER been able to handle?
Floyd has a tendency to get on the ropes. Cotto, De La Hoya, Maidana (in the first fight) all of them push him there for a great part of of their fight.
Cotto manage to find some success there too.
Duran is many times better infighter than all of them, with really heavy hands at welterweight. Watch any video of Leonard talking about the effect they had on him.
The biggest puncher he met at that weight according to his own words.
Duran was really good at driving people on the ropes and beat them in the body.
He could do this even in losing efforts. In his second fight with Leonard for example, he still rushed him several times in the ropes
and had success both downstairs and to his head, although Leonard did his best to be mobile every second of the fight.
Duran couldn't make the most of it though. He seemed low in energy and his punches didn't have any sting.
Plus Leonard unloaded powerful uppercuts and rights, something Mayweather can't do, both due to his style (light counters whose power is based mostly on timing)
and due to him not having much power at welterweight. I would compare Floyd's punching power at welterweight with Duran's at 168.
My point is that a motivated and well prepared Duran will spend a lot of time with Floyd at inside and let him have it.
Floyd wouldn't be able to stop this from happening.
Also Floyd wouldn't find it so easy to time him. Floyd is a master at setting the pace of the fight and breaking his opponent's rhythm. It's
what he does!
Duran had an awkward timing though and he was one of the best, if not the best, fainters in the history of the sport. He had many ways to open his opponent's defence.
Duran was a complete fighter imo. He could do anything. The best technician of the fabulous 4.
Something that became obvious when he became older and depended more on his technique.
Outclassing fighters that knocked both Hearns and Leonard out within a year difference.
There are videos with Barkley saying he was the best technician he fought.
It's not by accident that he is in so many top10 pound for pound lists and he is still absolutely loved by boxing "experts".
So at welterweight I could see Duran winning. He had the tools to beat anyone including Floyd.
Not that I count Floyd out. It would be a hell of a match. No way Floyd would school a top of his game Duran though.